In a shallow dish, mix 2 cups of room temperature water and 1 tablespoon kosher salt. Add the scallops and let soak in the brine for 10 minutes. Remove the scallops and dry as thoroughly as possible (any extra water causes the pan to spit when searing). Lightly season the scallops with 1 generous pinch of kosher salt.
In a medium stainless or cast iron skillet, heat the oil over high heat. Carefully add the scallops and cook without turning until an even brown crust forms on the bottom, 1 to 3 minutes depending on how high a heat your range provides. Flip the scallops using a fish spatula and cook on the other side until a crust just forms on the bottom and the center of the scallop is almost opaque, 1 to 2 minutes. Remove from the heat and transfer the scallops to a plate, leaving the juices in the pan.
Add the butter to the pan and melt it over medium-low heat. Add the garlic and oregano and cook until the garlic is lightly browned and fragrant, about 30 seconds. Add the heavy cream, milk and Parmesan cheese and simmer for 2 minutes, stirring occasionally and gently scraping the brown bits on the bottom of the pan. Add the spinach, sun-dried tomatoes and ¼ teaspoon of kosher salt and cook until the spinach is wilted, about 2 minutes. Return the scallops to the pan and warm for 30 seconds, spooning the sauce over the top. Serve immediately.